This invention relates generally to the reduction of particle contamination on wafers, and more specifically, to the use of thermophoresis to reduce particle contamination on wafers during wafer transport within a multi-chamber or multi-station substrate processing tool.
Integrated circuit (IC) processing technology is continuously concerned with reducing the feature size of components to increase the amount of circuitry that can be packed onto an integrated circuit of a given size and to increase the speed of operation by reducing the distance that signals need to travel within such circuits. Particulates with a diameter even several times smaller than the feature size of a component can cause failure of the IC if the particulate was present at a critical location during an important process step. This problem is particularly acute for large area ICs such as microprocessors and greater than four (4) megabit memories because such ICs have an increased area over which a critical defect can occur.
The multilayer structure of some ICs also increases the effect of particulates on yield because a particulate incorporated into one level of an IC can affect not only the circuitry of that level, but also circuitry on other levels. A defect in an embedded level of an IC can propagate through overlying areas, distorting the topography and thus disrupting operation of those circuit elements. For at least these reasons, it is important to minimize the amount of particulates that come into contact with a wafer immediately before and during processing.
FIG. 1 illustrates some common particulates and particulate sizes that are present in the ambient atmosphere. Expensive, intricate clean rooms and clean room procedures are used to significantly reduce the amount of airborne particulates to which a wafer is exposed during IC fabrication. Unfortunately, clean rooms cannot prevent particulates from being produced within an integrated circuit fabrication system, such as a multi-chamber or multi-station substrate processing tool.
Several techniques have been used within individual processing chambers within such tools to help reduce the likelihood of substrate contamination, including chamber cleaning procedures. For some processing procedures, the substrate is heated within the processing chamber which helps produce thermophoretic forces capable of repelling some contaminants away from the substrate.
However, contamination of wafers can be particularly acute during wafer transport, that is, during transfer of a wafer to the processing chamber or between chambers within a multi-chamber wafer processing system. During transport, the wafer may be exposed to different gases, possibly existing at different pressures and temperatures. These gases and the chambers possibly contain different particulate matter capable of contaminating the wafers. For example, a processing chamber may have a buildup of aluminum fluoride particles on the walls which can dislodge and contaminate a wafer being transferred into the processing chamber. Further, processing system components, such as robots, valves and the like, may generate particles, notwithstanding efforts to keep these components clean.